Synergistically tuned hydrogen storage thermodynamics and kinetics of Mg-Al alloys by Cu formed in situ mechanochemically

The high thermodynamic stability and unfavourable sorption kinetics during the formation of Mg hydride restrict its utilization, though Mg is environmentally friendly and abundantly available. In this paper, Cu formed in situ from mechanochemistry was introduced into Mg-Al alloys to tailor their hydrogen storage properties. The results showed that the onset desorption temperature was decreased from 295 °C for as-milled pure MgH₂ to 175 °C for as-milled Mg₉₀Al₁₀-Cu. The destabilization of MgH₂ was attributed to the formation of Mg-Cu and Mg-Al alloys during dehydriding. The phase structures and thermal analysis showed that the dehydrogenation of MgH₂ in the Mg₉₀Al₁₀-Cu was composed of the following three steps: the reaction between MgH₂ and Cu to form Mg₂Cu as the first step, the reaction between MgH₂ and Al to form Al₁₂Mg₁₇ as the second step, and the self-decomposition of the residual MgH₂ as the third step. The apparent activation energy for dehydriding was reduced from 148.8 ± 4.91 kJ mol⁻¹ for the as-milled pure MgH₂ to 112.1 ± 1.36 kJ mol⁻¹ for the Mg₉₀Al₁₀-Cu. The hydrogen absorption and desorption reaction enthalpies of Mg₉₀Al₁₀-Cu were decreased to 57.5 and 74.0 kJ mol⁻¹ H₂, respectively. The results indicated that the Cu formed in situ mechanochemically substantially improved the hydrogen storage thermodynamics and kinetics of Mg₉₀Al₁₀-Cu because the in situ-formed Cu and graphene nanoplates caused particle refinement.